Electrical potentiometer



Filed July 8, 1926 ZELL lL/J IN VEN TOR .L aua/z/ fw A TTORNEY in parallel relationship with each other is connected to the input circuit S1, one of these resistanoes being designated by the reference character R and the other by the reference character P. TWo movable arms are associated4 with'the resistance P. These arms move simultaneously, inwardly or outwardly, depending upon whether the potential ap- Vplied to the output circuit is to be decreased or increased, respectively. `Moreover,"thesey arms change the proportion of the resistance nected, by equal increments. These arms are also connected to the primary windingof the transformer T, the secondary winding of 'which is connected to the output circuit S2.

` In TEig. 2 similar reference characters are employed to designate parts similar to those of Fig. 1.* Accordingly, the reference charac- '20 ters S1 and S2 designate the input and output'circuits respectively, and the reference character T'designates the transformer'. The

Y "potentiometer of F ig. 2 comprises two resistanceswhich 'are also in parallel relationship with each other, the midpoint of one of these -resistances being grounded. This latter rel'sistance is divided into two parts and these "parts are identified by the reference charac- -ters M and N. The other resistance is identified by the reference character P'. An artificial network is interposed between the-inputV 'circuit S1 and the potentiometer. This net- -work comprises `equalser'ies resistance-elements R1 and R1 and equal shunt resistance elements R2 and R2. This artificial network is substantially free from inductive or capacivtative reactance. v Y

Theresistance P is connected to the primary winding of the transformer T. Owing 40 topractical limitations in transformer'design,

fthe inductive reactance oftheprimary windl' ing of the transformer T cannot be made as high asmaybe' desired. Now, if'a'constant *potential be applied at the source S1 and if its 745' frequency be varied, a varying current will Qflow'through the primary winding ofthe ,l atlow frequencies.V Moreover, if when the adjustment of the potentiometerischanged, Y

the impedance across which the primary winding of the transformer is connected' also `.changes appreciably, this will resultina cor- 160 responding change in the transmission-frequency characteristic of the system, the relative efliciency at they lower. frequencies vbeing 'i improved ifv the impedance Z1i'sl0wered.V

" More specifically, when theV adjustment of the potentiometer is increased or decreased there s by curve a the primary winding is connected is corre-.

spondingly increased or decreased. Yet in the' present inventionl the transmission-frequency characteristic curve remains prac- `tically the same throughout because kthe im- .VpedanCeZ1, across which the primary wind.-

ing ofthe transformer T is connectedpls inaintained substantially constant. P, across'which the output circuit S12-is conv The potentiometer of thisinvention is designed to provide negligible variations in impedance, or rather ja substantially constant impedance, Z1, which is the impedanceviewing the potentiometer 'from' the-*primary winding ofthe transformer T, for avlimited Vo'rpredetermined range of potentiometer adjustment.' That is to sayin accordance with his'invention the impedance Z1 is to remain substantially constantV at alltimes through- -out a'limited andv predetermined. range of loss introduced Vby thepotentiometer. Furthermore, the impedance Z2 which is the impedance viewing thepotentiometer'- from the vdirectionV of the input circuitjS1 is subs-tantially constant at a' predetermined *magniltud'e whenever the potentiometer is employed, as is usual, to adjust the gainof, for example, arepeater.' Y Y Y Fig.` 3 shows a number of curves indicating the lrelationship .between the impedanceV Z1 of the potentiometer andthe transmissiony loss introduced bythe potentiometer for va- Y,rions combinations of the elements of this invention. The straightline lcurve a shows an ideal condition in which the impedance Z1 is constant. Tf a potentiometer were designed having ythe ideal I characteristic curve represented by the reference character Y a,

the transmission at all frequencies would be modified bythe same magnitude when the position of the potentiometer arms was changed. y

Curve b shows the impedance-loss characteristic curve for-an old and well known potentiometer. impedance looking back toward the'potentiometer varies with the potentiometer adjust- Vment. Obviously,the results obtained with ftheold type ofvpotenti'ometer differed considerably from the ideal values represented p Curve o tiometer embodying theprmciples of this 1nvention. Thisv curve -indicatesvariations in vthe impedance presented to the transformer T which-differ by negligible amounts from thosey'presented :by vthe potentiometer of This curve-shows that the l :'120 represents a curve of apoten which curve a is characteristic.y lBy Suit-V able adjustments of the constants of the-potentiometer the curvature of curve c. may

be controlled iwithin suitable limits.` v

thenthe following relationship will exist:

In korder that the combination of the potentiometer and the shunt may receive waves from the circuit S1 without reflection losses,

the following relationship must exist:

RSR, p 12in-Z* '(2) o From these relationships itmay be readily shown that: i Y

Z :n '=.p{2m(1 -;n) -I- ai (3) In the potentiometers used heretofore, as already explained, the `ratio m was equal to .unity vand no shunt resistance such as R was used. Under these conditions -the impedance Z1 afell `off as yn decreased in magnitude from unity. The loss introduced between the circuit S1 and the transformer T increased as An was reduced.v Curve b of Fig. 3 shows the relationship between lthe impedance Z1 and `the ,loss n caused b turning down the p0- tentiometer. In t e practice of this invention, however, the resistance of the potentiometer P, as explained heretofore, is made .greater than the .impedance of the circuit S1. n other Words, m is made greater than unity. .It will .readily be seen that when the resistance .of the otentiometer P is made very great, the impedance@ will first. increase and then decrease as the value of n is decreased.

hereinabove, and ,is illustrated by curve c of Fig. A3. By choosing a suitable value for m, ithe maximum Value reachedby the impedance Z1, Las illustrated by curve rvc, will be within im Vcertain tolerable .limits which arey fixed by .the requirement that .the eiect of changing the 4potentiometer setting must be substantially the same -at'all frequencies of the transmittedciurent. By adoptinga suitable limit 1'5 for fthe variation of the potentiometer P, the

`This follows also from Equation 3, given variation of the impedance Z1 below the desired value can be kept within tolerable limits.

The potentiometer, of which c is the characteristic impedance-loss curve, introduces a transmission loss Within predetermined magnitudes. lVhen gain variations are desired in some other predetermined range, for example, in some lower range it becomes necessary to supplement the p0- tentiometer with the artificial network (Shown in Fig. 2) comprising series and shunt resistances. As is very readily understood, such a network introduces a transmission loss of .a definite magnitude. By employing resistance in such a network to the exclusion'ofl capacitative or inductive reactance the artificial network becomes distortionless, and thus does `not affect the transmission-frequency characteristic of the system. By employing different artificial networks to supplement the potentiometer, gain adjustments may be made overa considerable range, as may be required, and the impedance-loss curves may, at the same time, be made toassume the shapes of, for example, the curves d or Y The variations in the impedance Z1 presented to the transformer T by the potentiometer depend on the relative magnitudes of resistance P and impedance Z5. By varying the comparative magnitudes of the resistance P and the impedance Z5, the impedance-loss characteristic curve may be made to vary in shape. In the old and Well known type of potentiometer the resistance P was made equal'to the impedance Z5 so that the characteristic curve assumed the sha-pe of the curve o of Fig. 3. Moreover, by changing the ratio ofthe resistance P to the impedance Z5, the impedance Zl presented to the transformer T can be controlled to a considerable degree. The resistance R of Fig. l is bridged lacross the resistance P so that the impedance Z2 may be made as nearly equal to the impedance ZA1 as may be found desirable.

Whenever it becomes necessary to have impedances Zl and Z2 equal, the values of resistances R and P may be determined from the 'following equations:

Q 1 R Z2Q 1 and (4) in which Q-is the ratio Il. Z5

While the invention has been disclosed in certain particular arrangements for the purpose of illustration, it is to be understood that the general principles of this invention may the potentiometer.

thereto and so related to each other that their joint impedance substantially equals the impedance ofv said circuit, and means for adjusting the gain of the potentiometer, said means comprising two arms and an arrangement whereby said arms may determine and change the proportion of the potential drop across one ot said resistances to be delivered by said potentiometer.

'2. VA potentiometer free from Jfrequency discrimination interconnecting an input 'circuit and an output circuit, comprising two i'esistances in parallel'relationship with each other, and two movable arms associated with one of the resistances for Asimultaneously varying the effect of the latter resistance by equal increments, one `of said resistances being-greater than the impedance of said input circuit, said resistances exhibiting a magnitude substantially equal to the impedance of said inputcircuit. j

3, A potentiometer. interconnecting an input circuit and an output circuit, comprising two resistances in parallel relationship with each other, and two movable arms associated Vwith one of the resistances for simultaneously varying the potentialtherebetween by equal increments, the resistance with which the movable arms are associated having greater magnitude than the impedance of said input circuit, said input andoutput circuits. having at all times-substantially constant impedances when viewed from opposite sides of 4. A potentiometer Vfree from lfrequency discrimination connected across the terminals ofk an input circuit for varying the` voltage of said input circuit applied to an output circuit, comprising two resistances each of greater magnitude than the impedance of said input circuit, and moans for maintaining said potentiometer balanced while varyingthe voltage ofthe input circuit applied to the output circuit, said means including arrangements for varying the proportion of the potential drop across one of said resistances which shall be delivered to said output circuit.

5. A potentiometer interconnecting an input circuit and an output circuit, comprising two resistances in parallel relationship with each other, one of said resistances being grounded at its midpoint, and two movable arms associated with'the'other of Isaid resistances for simultaneously varying the voltage between said arms by equal increments, the latter resistance being greater than the iinpedanceoi said input circuit;

6. A potentiometer interconnecting an input circuitY and an output circuit, comprising two resistances in parallel relationship with each other each being greater than the impedance of said output circuit, two arms aSSO- ciated with one of said resist-ances, and means to simultaneously move said arms in order to vary the voltage set upby said latter resistance equally and in opposite directions, said i resistancesbeing so related that the impedanceloolring from the input circuit to the output circuit equals the impedance looking from the output-.circuit to the input circuit.

7. A system'for controlling the proportion of the voltage ot an input circuit'appg plied to an output circuit Vwithin a predetermined range, comprising an adjustable resistance of greater impedance than that of said input circuit ,and an-artilicial line including equal series lresistances andl equal f* Athe input circuit, andan artilicial line inter- -posedfbetween the parallel resistances and the input circuit, said artificial line including two equal series resistances aiidtwo ,equal 4shunt resistances and being employed :tor

shifting' the limits of voltage variation oi said parallel resistances to other Vlimits in the voltage spectrum. Y j

'9. A potentiometer interconnecting an input circuit and an output, circuit, compris- Ving two resistances in parallel relationship with each other, each oi said resistances being greaterV than the impedance of said in-V put circuit and each being so proportioned with respect to the other thattheir impeding the potentialv impressed on the output circuit by tlie input circuit, and an artificial line interposed between said input circuit and A El?, n

Vance substantially equalsthe impedance look- Y' ving into said input circuit, means tor adjust- Eil-in said two resistances in parallel relationship,

saidy artilicialfline comprising equal series Yresistance elements and equal shunt resistance elements, said'artilicial line introducing a loss ot Vpredetermined magnitude between 'the input circuit and the output circuit.

10. Apotentiometer interconnecting an inif des tra

put circuit and an output circuit, comprising two resistances in parallel relationship with each other, the joint impedance of said resistances being equal to the impedance of said input circuit said resistances individually exhibiting greater magnitudes than the impedance of said input circuit and their combined impedance terminating said input circuit without introducing reflection, means for adjusting within predetermined limits in the voltage spectrum the potential impressed on the output circuit by the input circuit, and means comprising equal series impedances and equal shunt impedances for shifting said predetermined limits in the voltage spectrum to other limits therein.

11. A system comprising two parallel resistances, one resistance being grounded at its midpoint, two movable arms associated with the other resistance, the latter resistance being greater in magnitude than the impedance of the circuit containing the source of energy and being so proportioned with respect to the first resistance that their combination terminates said circuit containing said source of energy without the introduction of reflection, each varying its effective potential magnitude equally with respect to the terminals of said resistance, and an artificial line comprising equal series resistance elements and equal shunt resistance elements,

- said system being substantially free from unbalanced currents.

12. A system for adjusting voltage within predetermined limits of variation without frequency discrimination. comprising two parallel resistances one of which is adjustable and has a greater impedance than the circuit transmitting energy thereto, and an artificial line including equal series resistances and equal shunt resistances, the loss characteristic of the artificial linev determining the limits of variation of the voltage.

13. A system for interconnecting an input circuit and an output circuit suitable for adjusting the voltage of the input circuit to be applied to the output circuit, comprising two parallel resistances and a resistance artificial line, said parallel resistances being individually greater than the impedance of said input circuit, the parallel resistances being so related that the impedance of the system viewed from the input circuit substantially equals the impedance of the system viewed from the output circuit.

14. A system for interconnecting an input circuit and an output circuit suitable for adjusting the voltage of the input circuit to be applied to the output circuit Without the introduction of noise, comprising two parallel resistances each of greater magnitude than the impedance of said input circuit and jointly terminating said input circuit without reflection, and an artificialline including equal series resistances and equal shunt resistances and introducing a loss of predetermined magnitude.

15. A system interconnecting an input circuit and an output circuit, comprising two parallel resistances, one resistance being grounded at its midpoint` means for simultaneously varying the effective magnitude of the other resistance by equal increments with respect to its terminals, the latter resistance being of a predetermined magnitude which is greater than the impedance of said input circuit, a balanced artificial line, means whereby said system is rendered substantially free from eddy currents.

16. A system interconnecting an input circuit and an output circuit, comprising two parallel resistances, one resistance being grounded at its midpoint, means for changing the effective magnitude of the other resistance by equal increments with respect to its terminals, the total magnitude of the latter resistance being greater than the impedance looking into said input circuit, an artificial line having equal series elements and equal shunt elements. and means whereby said system is rendered substantially free from eddy currents.

17. A balanced potentiometer interconnecting an input circuit and an output circuit for varying the gain of the output circuit, said potentiometer having two parallel elements of resistance each having an impedance greater than that of the input circuit and being so proportioned that the impedance presented to the output circuit substantially equals the impedance of the input circuit, said potentiometer presenting to the output circuit an impedance which increases to a small extent above a definite value and decreases below that value as the loss increases, the maximum departure from said definite value being within predetermined limits.

18. A potentiometer substantially free from frequency discrimination, comprising a plurality of parallel resistance elements bridged across a telephone line, one of which is greater than the impedance of the telephone line, said resistances conjointlv exhibiting an impedance equal to that of the telephone line, and means for adjusting the gain of the potentiometer, said means comprising two arms and arrangements to move said arms simultaneously over one of said resistances to vary the portion of the resistance included therebetween in such a way that the portions of the .resistance not included between said arms remain equal.

In testimony whereof, I have signed my name to this specification this 2nd day of July, 1926.

LEWIS L. BOUTON. 

